Extruding integrally stiffened panels



Sept. 6, 1955 s, REED EXTRUDING INTEGRALLY STIFFENED PANELS 2 Sheets-Sheet 1 Filed July 8, 1952 ATTORNEYS United States Patent EXTRUDING INTEGRALLY STIFFENED PANELS Macdonald-S; Reed, 'Erie, Pa.

Application July 8, 1952, Serial N o. 297 ,666,

7 Claims. '(Cl. 29-548) This invention relates to methods of forming metal sheets and particularlyto theforming of thin sheets having integral upstandingribs, usually referred to as in-. tegrally stiffened panels.

It is desirable, especially in the aircraft industry, to have sheets of relatively large surface area :and .quite thin provided with integral 'upstanding paralle1 ribs or flanges formed integrally therewith to provide stiffening. whereby such sheets may be .employedas a rigid-:skin for the aircraft. The production ofsuchstructural .sheets..has heretofore been impractical by knowntmethods. since .itis extremey difficult to produce an integral structure :having such ribs or flanges of the .requiredheight .orthickness. Attempts have been made to produce such shapes by forging and/ or milling, but such attempts. have provenimpractical or uneconomical. In general, it is desirable that 3 finished sheets of a thickness of theorder of magnitude of 1 inch be provided with integral ribs or flanges. of about the same thickness projecting from one surface and spaced apart from 1 /2 to 3 inches. The ribs are desirably of a height of the general order .of 1 inch or more. It can readily be seen that integral structural shapes of those dimensions are extremely difiicult to produ'ceby practical methods.

Attempts have previously been made to economically produce integrally stiffened panels of .the type described 4 but none of them have thus far proven successful. Applicant proposes to, produce such. panels. by extruding plastic material, such as metal, .to form a sheet having in+ tegral ribs projecting from one surfacethereof but to extrude such sheet with the webportionbetweenthe ribs corrugated or in folded conditionto occupy less space. The corrugated sheet thus extruded may be in the general form of 'a cylinder, spiral, ellipse, partlystrai-ght and partly curved, or may be sinuously arranged- After the sheet is extruded it is bent to define a generally .flat corrugated sheet having the required ribs extendingfrom'the crests or grooves of certain corrugations. The corrugations between the ribs are thereafter flattened, preferably by stretching the sheet in.a..transverse direction to form the finished product consisting of a flat .thin sheet having spaced parallel integral ribs projecting from one surface. The flattening of the cornugationsmay beaccomplished by stretching the sheet, as described, or may be accomplished by other means such as pressing or by means of suitably shaped rollers.

By extruding the sheet in corrugated form and further extruding the corrugated sheet in the form of a cylinder or the like a final product of' much greater width' than the actual width of the extruding die is possible.

It is therefore an object of this inventiontoprovide a method of forming stiffened panels more efiicientlyand more economically than by methods heretofore known.

Another object of this inventionistoprovide amethod of forming integrally stiffened .panels ofsheet metal of practical dimensions. 7

It is still another object of this invention to provide a method for forming sheet material whereby pieces of Patented Sept. 6,, 1955 2 greater. area may. be fabricated than viously known methods. v

A still further object of thisinvention his the provision of a method of forming an article with conventional apparatus resulting ina product of greater size than the capacity of the apparatus will permit producingdir'ectly.

Further objects and advantages will appearto-those skilled in the art as the description proceeds in connection with the accompanying drawings wherein:

Fig. 1 is a fragmentarysectiona-l view of .a-portion .of an integrally stiffened panel constituting the desired final product of the present invention; I

Fig. 2 is a fragmentary .elevational viewv of .a portion of an extruding die employed to practice the present invenpossible with pre tion;

Fig. 3 is a fragmentary sectional viewthrougha portion of an extruded sheet with the corrugations arranged reversely to those produced by :the dies .ofFig. -2;=

Figs. 4 and 5 illustrate other shapes of integrally stiff ened panels that may be readily produced-bylhe present method; I 3

Figs. 6 and 7 schematically illustrate possiblearrangements of the extruding openings. inaconventional die for thepractice ofthe present invntion; and,

Figs. 8, 9 and 10 are schematic-illustrations of an: extruded cylinder illustrating sequentially thesteps of bendingv and flattening the extrusion .to the finaldesired form.

The desired product shown in Fig. 1 comprises -a relatively thin continuous and substantially flat sheet orfskrin 2 preferablyof aluminum, aluminum alloy,'or--a suitable magnesium alloy for use ,in covering aircraft frames. The skin 2 has integrallyformed thereon spaced parallel :up standing ,ribs or flanges 4 joinedintegrallyytosone surface .of the skin 2. In. general a satisfactory stiifened panel may have a skinportiomof a thickness of the order *ofinch .with the ribs valso of about rlIlOh inth'ckness and-projecting outwardlyfromskin 2 adistanceuofthe order of- 1 inch; The=ribsmay be from: 1% w s inches apart, although in some applications itmay 'be desirable that the ribsrbeevencloser-.or'spaced apart a greater distance. Alsothe-thickness dimensions and the :height of theribs rmay yaryzwidelyto meet particularly requirements. r

Fig. 2 illustrates-a fragmentary Portion of an-extr-uding die, which may becther-wise of conventional construction to be-remployed in a..conventiona-l extnudingpress. in general, the-type of'press contemplated includesaa con tainer for metal having one wall defined at least inlpart by dies having openings therethroughthrou'ghwhiclrthe metal is-forced under pressure to issue-as anelongate structure. Thendies illustrated may comprise-separate portions 6 and-Shaving spaced apart edges 10and 12 defining. the opening: through which metal is: forced. As suggested-in Fig. 2 the extruding .openingsde'finean .elongated-sinuously arranged slot'designed toextrude a corrugated sheet having corrugations -.corre;sponding -to the portions 14 and 1.6. Thedie portionz6 is .also'pro videdwith slots 18 communicating withthe vcontinuous corrugated sheet openingto produce integral ribs .on-the extruded sheet. As shown the ribs will project upwardly from the base of grooves in. the extruded sheet with at least one corrugation 14 between 'adjacentribs- As also suggestedinFig. 2, the general configuration of the extruded sheetis' curved, which may be generally cylindrical or other similarshape to-define a corrugated cylinder having vintegralribs thereon.

Fig. 3 illustrates a modified form the extmdedprodtict may take wherein the ribs 18''. project upwardly from' the crests of adjacent corrugations '14 and whereintlic' cor rugated portions i6v extend away from the bases-of ribs 18'. This .form ofextrusion resultsin the *same final product as that of Fig. 2 but the dies for producing this extrusion are of considerably greater strength than those shown in Fig. 2 and may possibly be more economical to produce.

Figs. 4 and 5 illustrate alternative forms of finished product. Fig. 4 shows an integrally stiffened panel having a planar thin skin provided with spaced parallel upstanding ribs 21. Each of the ribs 21 has integral flange or cap portions 22 projecting laterally of the free edges thereof. It will be readily apparent that such shapes can be easily produced by extrusion but would be extremely 2 diflicult and expensive to produce in any other way. The form of Fig. 5 suggests a planar sheet or skin 24 having integral stiffening ribs 26 thereon, similar to Fig. l, but also including projections or stiffening members 28 projecting from the opposite surface of the sheet 24. Clearly such projections 28 may be opposite the bases of ribs 26 or may be intermediate the ribs and may he placed on either side of the sheet 24. Figs. 4 and 5 are merely illustrative of possible shapes, it being obvious that innumerable other sectional shapes may be readily produced.

Figs. 6 and 7 schematically illustrate extruding dies and suggest alternative arrangements of the extruding openings therein whereby an extrusion of relatively large transverse linear dimension may be arranged to be extruded from dies of limited size.

Fig. 6 shows a suitable supporting frame 30 to be attached to any suitable extruding machine in a known manner and which supports an extruding die 32. The die 32 is provided with a slot of the configuration shown at 34 and wherein the sinuous slot extends generally circularly around the face of the die. Fig. 6 shows only a portion of the extruding slot in solid line but it is intended that the slot continue around the dotted line area. It is possible that the die be provided with one or more obstructions 36 to produce a longitudinally split generally cylindrical extrusion (see Fig. 8) which may be readily bent out to a generally flat shape as shown in Fig. 9. However, if desired, the cylinder may be extruded without the obstruction 36 in the die to produce a continuous generally cylindrical surface which may be later split to permit opening and flattening of the extrusion in a manner to be described.

The extrusion from the dies shown in Fig. 6 is shown in fragmentary section in Fig. 3 and schematically in Fig. 8 wherein numeral 42 identifies the longitudinal split produced by the obstruction 36. It is generally of the shape of a corrugated cylinder with the corrugations 14 and 16' extending longitudinally thereof and with integral ribs 18 projecting from one surface. After the extrusion has issued from the dies of Fig. 6 the edges formed by the obstruction 36 may be pulled apart, as indicated by arrows A in Fig. 8, to flatten the extrusion to the form of a corrugated sheet wherein the crests of the corrugations lie in substantially parallel planes, as shown in Fig. 9.

Thereafter the free edges of the corrugated sheet are pulled apart, as indicated by the arrows B of Fig. 9, in a stretching operation and the corrugations 14 and 16 are thus straightened out or flattened to provide the product shown' in Fig. 1 and schematically in Fig. 10. Suflicient tension is applied to the sheet to straighten the corrugations to the form shown in Figs. 1 and 10 and to slightly exceed the elastic limit of the metal so that it acquires a permanent set in the planar shape shown.

A cursory inspection of Figs. 8 to 10 clearly illustrates how the finished panel of Fig. 10 is of a length many times the maximum diameter of the extruded cylinder of Fig. 8, thus permitting the production of a flat integrally stiffened panel of a width far greater than the direct capacity of the extruding die.

It is within the scope of the present invention to provide means to engage the extrusion as it issues from the die and continuously guide it to a flattened corrugated shape and to direct the edges outwardly away from each other to accomplish stretching simultaneously with the extrusion and thereby accomplish substantially continuous production of the desired integrally stiffened panels. A plurality of rollers, properly arranged, may be caused to engage portions of the extrusion as it issues from the die and direct it to its final shape. In such a case the flattening of the corrugations could be accomplished by opposed rollers between which the extrusion passes in a continuous manner.

Fig. 7 illustrates a still further modified arrangement of the extrusion opening in a die face. The frame 30 supports a suitable die plate 38 having the undulating extruding slot 39 arranged to follow a sinuous path 40 across the face of the die plate. Clearly such an arrangement will produce an extrusion which, when flattened and stretched, will result in an integrally stiffened panel of the type shown in Fig. l but of a width many times the width of the die plate 38. Thus integrally stiffened panels of practical widths may be produced by apparatus having relatively small die areas. Clearly many other arrangements of extruding openings are possible and the present invention is not limited to those shown. It is to be noted that the circular arrangement of Fig. 6 produces a cylinder having the integral ribs extending radially outwardly from the outermost crests of adjacent corrugations whereas the arrangement of Fig. 7 shows the corrugations extending between the ribs. The die arrangement of Fig. 7 is a more compact arrangement than that of Fig. 6 and permits a greater width of sheet to be extruded.

While a limited number of alternatives are shown and described herein it is to be understood that the invention is not limited thereto but may include other modifications falling within the scope of the appended claims.

I claim:

1. A method of forming an integrally stiffened panel comprising, the steps of; extruding a thin corrugated sheet of material having parallel spaced integral ribs on one surface thereof parallel to the corrugations, and thereafter flattening said corrugations to produce a wider and substantially flat panel having spaced parallel integral ribs upstanding from a surface thereof.

2. A method as defined in claim 1, wherein said corrugations are flattened by stretching said corrugated sheet in a direction transverse to said ribs.

3. A method of forming an integrally stiffened panel comprising, the steps of; extruding a thin sheet of material in the general form of an elongated cylinder having the wall thereof corrugated longitudinally and having spaced longitudinal ribs projecting from one surface thereof, opening said cylinder to form a generally flat corrugated panel, and thereafter stretching said corrugated panel in a direction transverse to said ribs to flatten said corrugations and form a thin flat panel having spaced parallel integral ribs projecting from one surface thereof.

4. The method defined in claim 3 including the step of longitudinally splitting said cylinder during the extrusion thereof.

5. A method of forming an integrally stiffened panel comprising, the steps of; extruding material in the form of a thin sheet with at least certain portions thereof curved to a generally cylindrical shape, said sheet having longitudinal corrugations and spaced integral ribs projecting from one surface thereof parallel to said corrugations, bending said sheet to form a generally flat corrugated sheet, and thereafter stretching said sheet in a direction transverse to said ribs and corrugations to flatten said corrugations to form a substantially flat thin panel having integral parallel ribs projecting from one of the fiat surfaccs thereof.

6. The method defined in claim 4, wherein said stretching step is performed by placing said sheet under suflicient tension to flatten said corrugations and thereafter to stretch said flat panel slightly beyond its elastic limit.

7. A method of forming an integrally stiffened panel comprising, the steps of; extruding a thin sheet of material to form a sinuously arranged wall within a relatively small transverse area, said wall being corrugated longitudinally and having spaced longitudinal ribs projecting from one surface thereof, bending said sinuous wall to form a generally flat corrugated panel, and thereafter stretching said corrugated panel in a direction transverse to said ribs to flatten said corrugations and form a thin flat panel having spaced parallel integral ribs projecting from one surface thereof.

UNITED STATES PATENTS Monterde Dec. 4, 1906 Rendleman Apr. 5, 1927 Gersman July 14, 1931 Otte Oct. 22, 1935 McKee Nov. 18, 1941 Davie, Jr. Jan. 11, 1949 Burke Nov. 11, 1952 

